In a camshaft adjusting device of the above type known from DE-OS 42 18 082, the required hydraulic pressure medium is fed into the device through a connecting bracket which is rotationally fixed to the driven unit and coaxially surrounds the end portion of the camshaft. The outer peripheral surface of this connecting bracket comprises a number of annular flanges between which the hydraulic pressure medium is guided in circumferential annular channels and which are sealingly surrounded by a reception bore of a connecting plate. The hydraulic medium flows via the control valve and through feed bores made in the connecting plate into the annular channels of the connecting bracket from where it is diverted through a longitudinal channel into a direction perpendicular to the camshaft adjusting direction. The sealing of the pressure medium conveying channels is achieved by steel sealing rings comprising a split gap and arranged in annular grooves in the outer peripheral surface of the annular flanges of the connecting bracket while bearing sealingly against the inner wall of the reception bore of the connecting plate.
Practice has shown, however, that in such sealing arrangements, the rotation of the driven unit is transmitted to the steel sealing rings which causes them to "dig" into the inner wall of the reception bore with their radial bearing surfaces, or the steel sealing rings and the reception bore undergo a considerable amount of wear. This detrimental behavior is due to frictional locking between the steel sealing rings and the inner wall of the reception bore resulting from the pressure of the hydraulic pressure medium prevailing in the annular channels and, more importantly, from the radial pre-stress of the steel sealing rings.
Measurements of the pre-stress of "dug-in" steel sealing rings have shown that the steel sealing rings can get buried to the extent that the pre-stress force becomes zero. This can result, for example, in a setting-free of scuffing chips which, on penetrating into the camshaft adjusting device, can cause a malfunctioning. Further, the "digging-in" of the steel sealing rings into the reception bore causes a radial expansion of the steel sealing rings which results in an enlargement of the split gap of the steel sealing rings arranged in the annular grooves and thus also in an enlargement of the leak gap of the steel sealing rings. Under certain circumstances, this can lead to a loss of pressure medium in the pressure chambers of the camshaft adjusting device during a standstill of the internal combustion engine, so that the adjusting piston is no longer sufficiently clamped hydraulically during starting of the engine and can abut unobstructedly against its end stops resulting in a disadvantageous generation of noise.
It was also determined that from a certain penetration depth of the steel sealing rings into the reception bore during operation of the engine especially at low engine speeds, vital system characteristic values such as, for example, the adjusting speed of the camshaft adjusting device, are strongly reduced because the additional pressure medium leakages and a limited performance of the pressure medium pump lead to a sinking of the pressure level. Even the use of steel sealing rings with a lower pre-stress force has not been able to substantially diminish the "digging-in" effect of the steel sealing rings because the attainable minimum pre-stress force is determined essentially by the toleranced inner diameter of the steel sealing rings, and the surface pressure of the steel sealing rings, especially in the presence of pressure medium pressure is, in any case, still so high that the aforesaid "digging-in" with its negative consequences continues to occur.